1. Field of the Invention
This invention relates to a process for thermo-chemically dewaxing hydrocarbon transmission conduits. More specifically, the present invention relates to a process for thermo-chemically dewaxing hydrocarbon transmission conduits which are either on the surface or subsea, the method being effected by injecting one or more emulsified beds of Nitrogen Generating System NGS plus heat while the emulsion breaking time is previously calculated so as to dissolve the maximum possible amount of the paraffin deposits within the conduit with simultaneous and safe removal of the fluidized paraffin deposit, such removal being effected co-currently to the production flow, so as to avoid the building up of non-fluidized plugs or deposits in the interior of the conduit.
2. Prior Art
The expression "hydrocarbon transmission conduits" is applied to any cylindrical means for transmitting hydrocarbons, either in the liquid or gaseous state, since the reservoirs wherefrom they are extracted and up to the christmas tree of the subsea well, or either up to the land wellhead, as well as since the subsea well christmas tree and up to the surface sea installations ("production platforms"), or else to any conduits connecting sea installations to terminals and for primary working station, and lastly to same connecting these stations to refineries and/or petroleum or petroleum-derived products processing plants, which can, due to several reasons, develop paraffinic deposits in their interior. On the other hand, in subsea conduits, according to the specific oil being produced, oil temperatures below the Initial Crystal Temperature ICT, as well as the hydrodynamical characteristics of production flow can cause the deposition of paraffins, asphaltenes and resins.
U.S. Pat. No. 4,755,230 to J. P. Ashton at al, of Jul. 5, 1988, relates to a process for dewaxing subsea conduits which comprises injecting an oil-in-water emulsion of an aqueous solution and a hydrocarbon solution, wherein the aqueous solution contains nitrogen and heat-generating reactants and a pH buffer to delay the delivery of heat and nitrogen up to the chosen point in the conduit where the reaction is to begin, whereby paraffin is made to melt. The hydrocarbon solution comprises the necessary amount of a solvent selected for its ability to dissolve the particular paraffins of the deposit, as well as a modifier selected to produce a minimal pour point for the paraffins involved in the deposit. When the action of the emulsified aqueous solution is over, it is pumped off, while the paraffin deposit is withdrawn together with the aromatic solvent. U.S. Pat. No. 4,755,230 does not provide any field application for the dewaxing of pipes using the suggested process. Thus, there is no disclosure in such patent concerning means of previously determining the paraffin percentage of the partially plugged pipe, neither the amount of removal of the paraffin (performance of the process).
Thus, there is a continuous need for processes which could bring solution to the problems still associated to the dewaxing of conduits, that is, processes precisely disclosed as regards field experiments, wherein conduits actually plugged by paraffin deposits would have accurately established the paraffin content in their interior, the performance of the process being precisely determined, besides the guarantee of safe operation, especially in places of difficult reach.
Therefore, one objective of the present invention is a thermo-chemical process for the dewaxing of hydrocarbon transmission conduits whereby the percentage content of paraffin in the interior of the conduit is previously determined by assessing the effective internal volume using a contrasting fluid, further, the effective internal volume is again evaluated in order to assess the dewaxing operation performance.
Another objective is to provide an oil-in-water emulsin between aqueous base fluids which contain the chemicals and the oil base fluid which consists in aliphatic and/or aromatic hydrocarbons and their mixtures, the emulsion being stabilized by the addition of a suitable surface agent, which promotes within the proper period of time, the coalescence of the aqueous phases, whereby an exothermic chemical reaction is produced between the reactants, under simultaneous and controlled release of nitrogen and heat, which combined to the hydrocarbon mixture promote the fluidization and removal of the paraffin deposit.
Another objective is to provide a process for dewaxing conduits wherein the fluid composition, as a water-in-oil emulsion, is made up as a function of the kind and concentration of the chemical additives so as to produce a safe mechanism of coalescence and breaking of the emulsions, leading to an accurate as well as precise release of the heat and nitrogen potentials of the emulsions, according to the dimensions of the conduit under dewaxing treatment and the limitations of the circuit as a whole.
Still another objective is to provide a process for the dewaxing of conduits which is effected gradually and co-currently to the production flow, avoiding the building up of undesirable paraffinic plugs which impair the displacement of fluids in the interior of the conduit during the dewaxing process or thereafter in the flow of the produced oil.